1. Field of the Invention
The present invention relates to an automatic detector for tire assembling-disassembling machines, particularly, but not exclusively, suitable for tire assembling-disassembling machines using a pair of arms each carrying a tire bead-releasing roll.
2. Description of Related Art
As it is known, tire assembling-disassembling machines have already been proposed having one or more bead-releasing rolls, which are carried at the free end of a respective telescopic support arm, arranged on opposite sides with respect to a tired wheel to be disassembled, and suitable for being pressed against the wheel tire to simultaneously release the tire bead at the two sides of the wheel, while allowing the tired wheel to rotate around its axis of rotation.
In order to carry out a bead-releasing operation with a pair of bead-releasing rolls, the operator, while taking into account the size of the wheel rim, controls the pair of bead-releasing rolls so as to move them close to a respective edge of the wheel rim, by causing an extension or lengthening of their telescopic support arms. When each bead-releasing roll reaches an abutting position against its respective rim edge, the operator also controls mutual approaching or “clamping” movement, of the two telescopic arms and thus of the bead-releasing rolls carried by them, while simultaneously setting in rotation the wheel the tire bead of which is to be released. Clearly, if all the manoeuvres have been correctly carried out by the operator, the edge of the two bead-releasing rolls should rest against its respective tire side, while abutting against the rim edge of the tired wheel.
In conventional tire assembling-disassembling machines, power is then applied to the telescopic arms, whereby the bead-releasing rolls are forced to get near to each other, while the tired wheel is rotating to complete a so-called bead-releasing operation. With tired wheels in use at present, such a bead-releasing operation can be carried out only with difficulty, as wrong setting of the bead-releasing rolls by the operator can cause serious damages, especially to tires having a lower outline and mounted onto a light-alloy wheel rim.
With more recent tire assembling-disassembling machines, in order to obviate such a drawback the so-called “dynamic bead-releasing” has been adopted, in the releasing of the tire carried out while the tired wheel is rotated so that each bead-releasing roll is moved both towards the axis of rotation of the wheel and closer to the other roll, thereby penetrating between tire bead and wheel rim edge while sliding on the tire bead preferably following a zig-zag path, which imitates the shape of the inner collar of the wheel rim, and thus each bead-releasing roll presses at the very tire bead and not on a tire side portion relatively far from the tire bead.
The path followed by each bead-releasing roll after its positioning close to its respective edge of the wheel rim is thus a broken line roughly having a first length parallel to wheel axis of rotation, a second very short length inclined and directed towards the same axis, and a third length also parallel to the axis of the tired wheel.
To allow each bead-releasing roll to follow the above described broken path, a plurality of structural solutions have been proposed for tire assembling-disassembling machines, as it is known to a person skilled in the art.
A first solution was a tire assembling-disassembling machine provided with cams arranged to control the bead-releasing rolls to follow a predetermined broken path. Such a solution, however, owing to the fact that the path is predetermined and fixed, cannot be adopted for all at present commercially available types of tired wheel.
A second and easier solution is to cause the bead-releasing rolls to follow an approaching path along an arched line in its respective lying plane containing both its respective telescopic arm and the tired wheel axis of rotation, starting from the wheel rim edge towards the axis of rotation of the wheel. With this structure, however, the bead-releasing rolls could start pressing onto a length of the tire side rather than onto the bead, which, as it is known, is the most resistant portion of the tire and thus with. the risk of causing the tire to break or to become permanently damaged.
A further already suggested solution is that such a broken path is manually executed by an operator, thereby entrusting the success of the tire bead-releasing operation to the skill and ability of the operator, who has to be highly trained.
A last solution is to provide that the bead-releasing rolls, after contact with the tire, press a spring and control a suitable detector in order to start the broken path. This solution has serious drawbacks in so far as the deformation calibration of the detector is concerned. As a matter of fact, if one is dealing with a soft or easily yielding tire, it might occur that a bead-releasing roll, when the same is in contact with the tire side, fails to control the detector which results in no control for starting the broken path being generated. The two rolls then continue their approaching movement, while further pressure is applied onto the tire side, which can sometimes results in the tire been damage or even cut.
If instead one is dealing with a hard or too rigid tires, the bead-releasing rolls could control in advance the detector, even before starting deformation of the tire side, whereby a control to start the broken path is generated too early. In this case, each bead-releasing roll will be forced to slide onto the tire side until it steps or passes over the wheel rim edge, which might results in both the tire and the wheel rim being damaged, especially if the latter is made of a light alloy.
Finally, it should not be forgotten that in all the above described tire assembling-disassembling machines one of the two bead-releasing rolls cannot be seen by the operator during a standard tire bead-releasing procedure since it is hidden from sight by the tired wheel and this results in a further margin of uncertainty and error.